Electric circuit breaker with overcenter acting type mechanism and contact adjustment



y 26, 1966 G. E. GAUTHIER ET AL 3,263,051

ELECTRIC CIRCUIT BREAKER WITH OVERCENTER ACTING TYPE MECHANISM AND CONTACT ADJUSTMENT Filed Feb. 5, 1963 2 SheetsSheet 1 FIG. I

IN VEN TORIS GEORGE. E. GAuTHIER, CHARLES F. HOBSON JR.

ATTORNEY July 26, 1966 e. .GAUTHIER ETAL 3,263,051

ELECTRIC CIRCUIT AKE IT VERCENTER ACTING TYPE MECHANISM AND NT ADJUSTMENT Filed Feb. 5, 1963 2 Sheets-Sheet 2 INVENTORS GEORGE E.GAUTH1ER, CHARLES F. HoasoN JR.

ATTORNEY United States Patent 3,263,051 ELECTREQ CERCUIT BREAKER WHTH UVERCEN- TER ACTING TYPE MECHANISM AND CON- TACT ADJUTMENT George E. Gauthier, Piainville, and Charles F. Hobson, In, Southington, Conn, assignors to General Electric Company, a corporation of New York Filed Feb. 5, 1963, er. No. 256,329 4 Claims. (Cl. 209-170) Our invention relates to electric circuit breakers, and more particularly to electric circuit breakers of the type including a pivotally supported contact arm actuated by an overcenter-acting type mechanism which in turn is operated by an overcenter type operating spring. One type of such mechanism includes a collapsing toggle linkage, the knee pin of the toggle being moved by a tension spring. Another type of such overcenter-acting is the cam and roller type mechanism such as shown for example in application S.N. 241,304 filed November 30, 1962, and assigned to the same assignee as the present invention.

For purposes of providing adequate contact pressure, and also for securely retaining the movable contact arm in the closed circuit position against vibration, shock, and high magnetic forces such as associated with short-circuit currents, it is desirable that operating mechanisms of the type described -be so arranged that in the on position, the toggle links operating the contact arm are substantially in the straightened or set condition. Since the mechanism is operated by an overcenter type of operating spring, however, only a fixed, predetermined amount, of force is available for moving the toggle linkage to straightened condition after the operating spring has gone overcenter. Since this force is limited, there is a particular optimum point of movement at which the movable contact should engage the stationary contact in order to build up the proper wear allowance, i.e., releasable compression of the contact pressure spring to allow for wear, by the time the toggle linkage has moved to fully straightened position and also to build up the required contact pressure. Thus, if the contacts engage too early during the movement of the mechanism, the operating springs may not have enough power to move the operating linkage to fully straightened or set condition, that is, the mechanism will not toggle. On the other hand, if the contacts do not engage early enough during the sequence of movement of the mechanism toward on position, there may not be enough travel remaining after the contacts meet to build up the required wear allowance or contact pressure. It is very desirable therefore that some means he provided for adjusting the mechanism so that the point in the movement of the mechanism in which the contacts actually first engage may be adjusted.

In accordance with the prior art, adjusting means have been provided by means carried by the movable contact arm, such, for example, as a threaded stud carried by the movable contact member and extending through an opening in the contact arm proper and a nut carried by the stud which provides an adjustable stop on the stud to limit the distance which the movable contact can move with respect to the main contact arm. It will be observed, however, that when the required adjustment is obtained in this manner, the free length of the contact pressure spring between the movable contact and the contact arm is altered. This decreases the force biasing the movable contact toward closed condition at the time the contacts first meet. In other words, although the contact pressure in the closed circuit position is unaffected by this adjustment, the gradient or rate of build-up of pressure from initial contact to closed position is decreased, whereas a steep force gradient is desirable, as will be more fully described hereinafter.

It is an object of the present invention to provide an electric circuit breaker including an operating mechanism of the overcenter spring toggle type including means for readily adjusting the point in the movement of the mechanism at which the movable contacts engage the stationary contacts, which is relatively simple and inexpensive.

It is another object of the invention to provide an elec tric circuit breaker of the type described including means for adjusting the point in the movement of the mechanism at which the movable contacts engage the stationary contacts without altering the minimum-stress (i.e., open-circuit position condition) of resilient biasing means biasing the movable contacts of such circuit breaker.

It is a further object of the invention to provide a mechanism of this type including such adjustment means which shall be accessible for manipualtion from the top of the breaker when the breaker cover is removed and which may be adjusted while the movable contacts are in the closed-circuit position.

It is another object of the invention to provide means for adjusting the wear allowance of circuit breaker contacts in the overcenter spring toggle type mechanism which can be adjusted to vary the relative heights of a plurality of individual stationary contact segments.

In accordance with the invention in one form, an electric circuit breaker is provided. comprising an overcenter spring toggle type operating mechanism adapted to operate at least one movable contact arm. The movable contact arm carries at least one movable contact member mounted on the contact arm so as to be resiliently movable, with respect thereto, a predetermined limited amount. The amount of wear allowance and contact pressure provided in the mechanism is adjusted, in accordance with the invention, by adjusting the normal position of the stationary contact supporting member with respect to a common insulating base which supports it and the operating mechanism.

In a particular form of the invention, the relatively stationary contacts are supported upon an elongated rigid supporting strap, which is mounted on an insulating base by means allowing a small degree of movement at one end thereof and which includes at least one set screw carried by the other end adjacent the contact portion and engaging the insulating base to vary the spacing of the supporting strap from the insulating base, combined. with clamping means for clamping the end of the contact strap with respect to the base after such adjustment is achieved.

The invention will be more fully understood from the following detailed description, and its scope will be pointed out in the appended claims.

In the drawings,

FIGURE 1 is a side elevation view of an electric circuit breaker incorporating the invention, shown in the closed condition;

FIGURE 2 is a side elevation view, on enlarged scale, of the contact portion of the circuit breaker of FIGURE 1, shown in the open condition;

FIGURE 3 is a top plan view of a portion of the circuit breaker of FIGURE 1, showing the end portion of the movable contact arm and the corresponding portion of the stationary contact supporting member in the closed circuit position;

FIGURE 4 is a sectional view taken substantially on the line 4-4 of FIGURE 2;

FIGURE 5 is a top plan view of the end portion of the stationary contact supporting member of the circuit breaker of FIGURE 1, and

FIGURE 6 is a fragmentary side elevation view of a portion of a modified form of the invention.

In the drawings, the invention is shown as incorporated in a three-pole electric circuit breaker comprising an outer or main casing of molded insulating material including a base 10 and a cover 11.

Mounted on the base 10 at one end thereof are three load terminals 12 (only one shown) and, at the opposite end of the base 10, three line terminals 13 (only one shown). The line terminals 13 are each connected to and supported on an end portion of a stationary cont-act supporting strap 14. Each of the stationary contact supporting straps 14 carries at its other end a pair of side-by-side stationary main contacts 15 (only one shown) and a stationary arcing contact 16, the three contacts being arranged in a triangular configuration as shown particularly in FIGURE 5.

Each of the main and arcing contacts 15 and 16 of each pole cooperates with a corresponding movable main contact 17 and a movable arcing contact 18 respectively. Each of the three movable contacts 17 and 18 of each pole is independently movable and is pivotally supported on a common .pivot pin 19 carried by the movable contact arms 19. Each of the movable contacts is also biased away from the contact arm 19 by a separate contact pressure spring 17 and 18'. In the open circuit position, rotation of each of the movable contact members about the pivot pin 19' is limited by engagement of the inner end portion 17A, 18A thereof with the underside of the contact arm 19.

Each movable contact arm 19 is pivotally supported in the circuit breaker base 10 by suitable means such as by a pivot pin 20. The movable contacts 17 and 18 of each pole of the circuit breaker are connected, by means of multiple strand flexible braids 21, to one terminal 22 of a trip unit 23, and the corresponding load terminal 24 of the trip unit 23 is connected directly to the main load terminal 12 of the circuit breaker.

For the purpose of moving the movable contact arms 19, together with the movable contacts 17 and 18, into and out of engagement with the stationary or line contacts 1S and 16, both manually and automatically, there is provided an operating mechanism indicated generally at 25. The operating mechanism 25 includes a generally U-shaped supporting frame 26 (only one side shown), the movable parts being pivotally supported between the opposite sides thereof.

The contact arms 19 are adapted to be rotated about their pivotal support pins 20 by means of a toggle action linkage including toggle links 27 and 28 connected together at a toggle knee point 29, and supported at the upper end on a pivot pin 30 carried by a releasable toggle carrier 31. The toggle carrier 31 is pivotally supported by the frame 26 on a pivot pin 313. The toggle links 27 and 28 are operated between straightened and collapsed positions by means of an operating handle 32 in cooperation with a vpair of tension type operating springs 33 interconnected between the handle 32 and the knee point 29 of the toggle linkage 27, 28. When the handle member 32 is in the on position as shown in FIGURE 1, the contacts are in closed position, and when the handle is moved counterclockwise from this position toward the left end of the breaker as viewed, the contacts are moved to the open circuit position.

The end 31 of the releasable toggle carrier 31 is formed to serve as a latching element and to engage an intermediate latch member 34 which is pivotally supported on a pin 35 carried by an extension 26' of the frame 26. The action of the tension spring 33 is such as to bias the toggle carrier 31 for rotation in a clockwise direction about its pivot 31B. The toggle carrier 31 is restrained from movement in such a direction, however, by its engagement with the intermediate latch member 34. A biasing spring, not shown, constantly urges the intermediate latch 34 in a clockwise, latching, direction as viewed. By reason of the greater force exerted on it by the toggle carrier 31, however, the intermediate latch member 34 is biased in counterclockwise direction whenever the breaker is latched, as shown in FIGURE 1.

For the purpose of normally restraining the intermediate latch member, and therefore the toggle carrier 31 and the operating mechanism as a whole, in the on position except in the case of predetermined overload current conditions, there is provided a trip unit indicated generally at 23. The particular construction and operation of the trip unit is not critical to the present invention, and any suitable type may be used. A particular trip unit which may be used, for instance, is shown in Patent No. 2,884,497, H. M. Steven et al., issued April 28, 1959, and assigned to the same assignee as the present invention.

The trip unit 23 includes a latch member 36 adapted normally to prevent the intermediate latch member 34 from rotating in a counterclockwise direction. The latch member 36 is pivotally supported on the trip unit 23 on a pivot pin 37 extending through aligned openings in a. boss 38 of molded insulating material integral with the housing of the trip unit 23.

The latch member 36 carries a latch roller 39 supported on a pin 40 extending between opposed spaced apart portions of the latch member 36. The intermediate latch member 34 is provided with a cam surface 41 which, when the breaker is latched as shown in FIGURE 1, bears against the roller 39 and biases the latch member 36 in a counterclockwise direction, that is, to the left as viewed in the figures. Latch member 36 is prevented from moving to the left by means, not shown, which is releasable by current-responsive means upon the occurrence of predetermined current conditions. When released by such current responsive means, the latch 36 moves to the left, allowing the intermediate latch member 34 to rotate counterclockwise, releasing the carrier 31. When the toggle carrier 31 is released from the intermediate latch 34, the carrier 31 is rotated in counterclockwise direction by the action of the main operating springs, permitting the toggle assembly 27, 28, and therefore the movable contact arms 19, to move upwardly toward open circuit position, the toggle links simultaneously collapsing to the left as viewed.

The breaker is reset by moving the handle 32 manually to the left as viewed to, and slightly beyond, the normal off position. During this movement, a portion 32' of the handle engages the carrier 31 and rotates it counterclockwise. When the latch tip of the carrier 31 engages the intermediate latch 34, further counterclockwise movement of a carrier causes the intermediate latch 34 to move to the left as viewed with the combined pivoting and sliding action. The latch 31 of the carrier 31 then clears the latch surface of the intermediate latch 34, and the intermediate latch is returned to its normal position by the action of its bias spring, thereby relatching the breaker.

When the mechanism is moved to the on position as shown in FIGURE 1, following resetting, the toggle links 27 and 28 are moved to the straightened condition, their movement in this direction being limited by engagement with the portion 31A of the releasable member 31, near the knee pin 29 of the toggle linkage. The final position of thecontact arm 19 is therefore determined by the construction of the mechanism and the location of its various pivot points, together with the length of the toggle links 27, 28.

For the purpose of providing contact pressure in this position, individual compression springs 17' and 18 are provided for the movable contacts 17, 18. It Will be observed therefore, that the maintenance of proper contact pressure, which depends on proper amount of compression of the springs 17, 18, requires that the movable contacts 17 and 18 be moved at least a finite small amount with respect to the contact arm 19 after initial engagement of the contacts 17 and 18 with the stationary contacts 15 and 16.

In addition, it must be anticipated that normal usage of the device will cause some erosion of the meeting contact faces. If not enough travel or wear allowance is provided, such erosion may permit the movable contact members 17 and 18 to rotate about their pivotal support w on the contact arm 19 enough to permit the back end 17A, 18A, of the contacts to engage the upper inner side of the contact arm 19. If this occured, substantially all contact pressure or even circuit continuity would be lost and serious heating or other difficulties could occur.

At the same time, it is not possible to provide a safety margin, to protect against this possibility, by providing an extra long amount of travel of the contact members 17 and 18 with respect to the contact arm 19. If this were done, it would cause the movable contacts 17 and 18 to engage the stationary contacts at a point in the operation of the mechanism when the toggle links are still a substantial distance from their straightened condition, and at a time when the mechanical advantage of the force provided by the operating springs 33 is rather low. As a result, under these conditions, it may be found that the operating springs 33 are not strong enough to then move the toggle linkage to full straightened condition. It is usually not possible, furthermore, to provide operating springs 33 of greater force in the space available. Also, it may not be practical to reduce the strength of the contact springs 17, 18' because of current carrying requirements.

In accordance with the invention, the point in the movement of the mechanism at which the movable contacts engage the stationary contacts may be accurately controlled. This is accomplished by a special mounting of the supporting strap 14 in the insulating base 10. Thus a pair of set screws 14 are provided, carried by the sup porting strap 14- adjacent each of the stationary contacts 15, and bearing against the insulating material of the base beneath the strap 14. In addition, the strap 14 is held with respect to the base 10 at its outer end by means of two screws 40 which pass through enlarged holes 41 in the insulating base 10 and threadedly engage the strap 14. A third or clamping screw 42 is also provided, extending upwardly through the insulating base 10 and into threaded engagement with the strap 14 between the set screws 14, see FIGURE 5.

In use, when the circuit breaker is first assembled, the mechanism is placed in the closed position and the distance of the movable contacts 17 and 18 from the contact arm 19 is carefully measured. This measurement may, if desired, be compared to the corresponding distance when the contacts are open, to indicate actual amount of compression. The set screws 14 are then adjusted to provide the required adjustment or correction. This may readily be done, since the amount of adjustment obtained is fixedly related to the pitch of the thread of the set screws. Thus in a particular embodiment a thread of the set screw 14" is used such that one complete rotation of the screw 14 alters the height of the supporting strap 14 by inch. When the height of the stationary contacts has been adjusted in this manner within the desired limits, the parts are locked in this position by tightening the locking screw 42. Alternatively, the parts may be locked by staking or cementing the adjustment screws, 14' with respect to the strap 14.

The hole 41 for the screws 40 at the outer end of the contact strap 14 are preferably made larger than the body of the screw 40 to permit the slight amount of angular movement which takes place as the adjustment of the contact end of the strap is carried out. It is not, however, necessary to loosen and retighten the screws 40.

It will be observed that by means of the present invention, the point in the operation of the mechanism at which the contacts first engage may be adjusted without changing the length of the spring 18' in the minimumstress, i.e., open-circuit position, of the contact arm. With a given circuit breaker mechanism, having predetermined operating springs, it is possible to predict at what point in the travel of the mechanism the contacts should engage. Contact pressure springs may be selected which will deliver the desired contact pressure with the amount of compression provided by the remaining amount of movement of the mechanism. Without changing any of theserelationships, it is possible, with the present invention, to adjust the breaker so that the contacts do, in fact, engage at the point in the travel of the mechanism previously determined to be desirable.

By reference to FIGURE 4, it will be observed that if the contact arm 19 should become canted or twisted slightly, the adjusting mechanism provided by the present invention will operate to equalize the wear allowance of both contacts 17. Thus the net result of an adjustment in this case might be that the supporting strap 14 itself becomes adjusted to a slight angle A conforming to the angle A of the contact arm thus providing equal wear allowances even though the contact arm should be tilted or twisted slightly.

It Will be noted that by reason of the particular adjusting means used, i.e., an adjustable set-screw acting between the contact supporting strap 14 and the base 10, the contacts 15 and 16 are at all times provided with a support or backing which serves to transmit force exerted on the stationary contacts directly to the base 10. This provides a strong and highly impact-resisting structure.

It has been found that with one commonly used molded insulating material, i.e., glass fiber filled polyester, the set screws 14' may be permitted to bear directly on the insulating material, and the device operated repeatedly without the screws being forced into the material. Thus for example in a particular embodiment, with contact pressures approximately 30 pounds per pole the contacts were 0perated through on-otf cycles 10,000 times without any perceptable indentations caused by the set screws 14' in the molded insulating base 10. If desired, however, and particularly if other insulating materials are used, a protective pad 45 of metal may be provided under the screws 14' such for example as shown in. FIGURE 6. The pad may comprise an elongated generally rectangular piece extending across the contact strap 14 and under both of the set screws 14. The pad 45 may conveniently be retained in place by the side walls of the pole chamher and by providing a hole, not shown, generally centrally thereof, into which the end of screw 42 can project.

While the invention has been shown in one specific embodiment, it will be apparent that many modifications thereof may readily be made. We therefore intend, by the appended claims, to cover all such modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electric circuit interrupter comprising:

(a) a support,

(b) at least one stationary contact,

(c) at least one movable contact arm pivotally supported on said support and movable between open and closed circuit positions with respect to said stationary contact,

(d) means for operating said movable contact arm between said open and closed circuit positions comprising a first link pivotally connected to said contact arm, a second link pivotally supported on a bearing normally stationary with respect to said support, said first and second toggle links being interconnected by a knee toggle pin,

(e) an operating member movably supported on said support,

(f) means for operating said toggle linkage between collapsed and straightened conditions to move said contact arm between said open and closed circuit positions respectively comprising overcenter spring means acting between said operating member and said toggle knee pin, and

(g) means supporting said stationary contact on said support comprising an elongated contact strap,

(h) means attaching one end of said contact supporting strap to said support member while allowing limited relative pivotal movement therebetween, said stationary contact being mounted adjacent the opposite end of said strap,

(i) means attaching said opposite end of said strap to said support comprising at least one set screw threadedly engaged in said supporting strap and including an end portion bearing against said support member whereby to adjustably space said second end from said support member and to directly transmit force exerted on said relatively movable stationary contact to said support member,

(j) and separate screw threaded attaching means attaching said second end of said contact strap to said contact supporting member adjacent said set screw.

2. An electric circuit interrupter comprising:

(a) a support,

(b) at least two stationary contacts,

(c) at least one movable contact arm pivotally supported on said support and movable between open and closed circuit positions with respect to said stationary contact,

((1) means for operating said movable contact arm between said open and closed circuit positions comprising a first link pivotally connected to said contact arm, a second link pivotally supported on a bearing normally stationary with respect to said support, said first and second toggle links being interconnected by a knee toggle pin,

(e) an operating member movably supported on said support,

(f) means for operating said toggle linkage between collapsed and straightened conditions to move said contact arm between said open and closed circuit positions respectively comprising overcenter spring means acting between said operating member and said toggle knee pin, and

(g) supporting means for said stationary contacts comprising an elongated conductive strap,

(h) anchoring means anchoring a first end of said strap to said support member while permitting limited pivotal movement therebetween,

(i) said stationary contacts being supported on said strap in side-by-side relation adjacent the end of said strap opposite said first end,

(j) a pair of set screws threadedly carried by said supporting strap adjacent said relatively stationary contacts respectively, each of said set screws including a portion projecting through said supporting strap and into engagement with said supporting member and being adjustable to vary the spacing of said supporting strap from said supporting member, and

(k) separate screw threaded anchoring means attaching said other end of said supporting strap and said supporting member together adjacent said relatively stationary contacts.

- 3. An electric circuit interrupter comprising:

(a) a support,

(b) at least two stationary contacts,

(c) at least one movable contact arm pivotally supported on said support and movable between open and closed circuit positions with respect to said stationary contact,

((1) means for operating said movable contact arm between said open and closed circuit positions comprising a first link pivotally connected to said contact arm, a second link pivotally supported on a bearing normally stationary with respect to said support, said first and second toggle link being interconnected by a knee toggle pin,

(e) an operating member movably supported on said support,

(f) means for operating said toggle linkage between collapsed and straightened conditions to move said contact arm between said open and closed circuit positions respectively comprising overcenter spring means acting between said operating member and said toggle knee pin, and

(g) supporting means for said stationary contacts comprising an elongated conductive strap,

(h) anchoring means anchoring a first end of said strap to said support member while permitting limited pivotal movement therebetween,

(i) said stationary contacts being supported on said strap in side-by-side relation adjacent the end of said strap opposite said first end,

(j) a pair of set screws threadedly carried by said supporting strap adjacent said relatively stationary contacts respectively, each of said set screws including a portion projecting through said supporting strap and into engagement with said supporting member and being adjustable to vary the spacing of said supporting strap from said supporting member, and

(k) a threaded stud extending through a clearance hole in said support member and into threaded engagement with said other end of said supporting strap, said stud having a headed portion at the underside of said support member.

4. An electric circuit interrupter comprising:

(a) a support,

(b) at least two stationary contacts,

(c) at least one movable contact arm pivotally supported on said support and movable between open and closed circuit positions with respect to said stationary contacts,

(d) means for operating said movable contact arm between said open and closed circuit positions comprising a first link pivotally connected to said contact arm, a second link pivotally supported on a bearing normally stationary with respect to said support, said first and second toggle links being interconnected by a knee toggle pin,

(e) an operating member movably supported on said support,

(f) means for operating said toggle linkage between collapsed and straightened conditions to move said contact arm between said open and closed circuit positions respectively comprising overcenter spring means acting between said operating member and said toggle knee pin, and

(g) supporting means for said stationary contacts comprising an elongated conductive strap,

(h) anchoring means anchoring a first end of said strap to said support member while permitting limited pivotal movement therebetween,

(i) said stationary contacts being supported on said strap in side-by-side relation adjacent the end of said strap opposite said first end,

(j) a pair of set screws threadedly carried by said supporting strap adjacent said relatively stationary contacts respectively, each of said set screws including a portion projecting through said supporting strap 2,520,258 8/1950 Pittman et a1.

and into engagement with said supporting member 2,699,479 1/1955 Gorham 200-466 and being adjustable to vary the spacing of said 2,921,169 1/1960 Judd et a1 200-153 supporting strap and said supporting member; and 2,932,704 4/1960 Dennison et a1. 20087 (k) a pressure plate beneath said second end of said 5 2,958,744 11/1960 Engle 200-166 supporting strap, said set screws bearing on said pressure plate Primary Examiner.

BERNARD A. GILHEANY, KATHLEEN H. CLAFFY,

References Cited by the Examiner UNITED STATES PATENTS 10 D. SMITH, JR., Assistant Examiner. 1,912,776 6/1933 Kuhn 200-165 Examiners. 

1. AN ELECTRIC CIRCUIT INTERRUPTER COMPRISING: (A) A SUPPORT, (B) AT LEAST ONE STATIONARY CONTACT, (C) AT LEAST ONE MOVABLE CONTACT ARM PIVOTALLY SUPPORTED ON SAID SUPPORT AND MOVABLE BETWEEN OPEN AND CLOSED CIRCUIT POSITIONS WITH RESPECT TO SAID STATIONARY CONTACT, (D) MEANS FOR OPERATING SAID MOVABLE CONTACT ARM BETWEEN SAID OPEN AND CLOSED CIRCUIT POSITIONS COMPRISING A FIRST LINK PIVOTALLY CONNECTED TO SAID CONTACT ARM, A SECOND LINK PIVOTALLY SUPPORTED ON A BEARING NORMALLY STATIONARY WITH RESPECT TO SAID SUPPORT, SAID FIRST AND SECOND TOGGLE LINKS BEING INTERCONNECTED BY A KNEE TOGGLE PIN, (E) AN OPERATING MEMBER MOVABLY SUPPORTED ON SAID SUPPORT, (F) MEANS FOR OPERATING SAID TOGGLE LINKAGE BETWEEN COLLAPSED AND STRAIGTHENED CONDITIONS TO MOVE SAID CONTACT ARM BETWEEN SAID OPEN AND CLOSED CIRCUIT POSITIONS RESPECTIVELY COMPRISING OVERCENTER SPRING MEANS ACTING BETWEEN SAID OPERATING MEMBER AND SAID TOGGLE KNEE PIN, AND (G) MEANS SUPPORTING SAID STATIONARY CONTACT ON SAID SUPPORT COMPRISING AN ELONGATED CONTACT STRAP, (H) MEANS ATTACHE ONE END OF SAID CONTACT SUPPORTING STRAP TO SAID SUPPORT MEMBER WHILE ALLOWING LIMITED RELATIVE PIVOTAL MOVEMENT THEREBETWEEN, SAID STATIONARY CONTACT BEING MOUNTED ADJACENT THE OPPOSITE END OF SAID STRAP, (I) MEANS ATTACHING SAID OPPOSITE END OF SAID STRAP TO SAID SUPPORT COMPRISING AT LEAST ONE SET SCREW THREADEDLY ENGAGED IN SAID SUPPORTING STRAP AND INCLUDING AN END PORTION BEARING AGAINST SAID SUPPORT MEMBER WHEREBY TO ADJUSTABLY SPACE SAID SECOND END FROM SAID SUPPORT MEMBER AND TO DIRECTLY TRANSMIT FORCE EXERTED ON SAID RELATIVELY MOVABLE STATIONARY CONTACT ON SAID SUPPORT MEMBER, (J) AND SEPARAT SCREW THREADED ATTACHING MEANS ATTACHING SAID SECOND END OF SAID CONTACT STRAP TO SAID CONTACT SUPPORTING MEMBER ADJACENT SAID SET SCREW. 